This invention relates to a vehicle attitude control method for effectively preventing an abrupt change of the vehicle attitude which is likely to occur as a result of an acceleration slip control for a vehicle.
For controlling acceleration slip, i.e., slip of drive wheels when a vehicle is suddenly started or accelerated, various methods have been proposed such as an acceleration slip control utilizing a well-known oil pressure circuit for anti-skid control in Japan Patent Application No. Sho 59-199216 and another acceleration slip control in Japan Patent Application No. Sho 59-199217 in which a wheel cylinder of a drive wheel is actuated by oil pressure from the pressure source for power steering so as to control the acceleration slip.
Furthermore, as a vehicle attitude control method for preventing an abrupt change of the vehicle attitude, such an application has been proposed in Japan Patent Application No. Sho 59-27651 that the suspension characteristic is altered to preferentially keep the stability of the vehicle in response to various driving conditions, e.g., sudden starting, sudden braking, sudden turning and high-speed running.
The above-mentioned prior art, however, include some problems as will now be discussed.
When the acceleration slip control is performed by utilizing a brake installed in the vehicle, drive wheels are affected by drive force and brake force at the same time. Namely as shown in FIG. 3, a drive wheel c of a vehicle b moving in the direction of arrow a is actuated by drive force F1 which is generated by a revolution power transmitted from an engine via an axle shaft d. On the other hand, in the case of controlling acceleration slip, brake force or friction force F2 is applied to a road contact-point e of the drive wheel c by the action of a brake. As a result, the angular moment M shown in the following formula is generated around the central point of the revolution g of a suspension arm f; EQU M=F2.times.r2-F1.times.r1 (1),
where r1 and r2 represent the distance between the central point g and respective force vectors F1 and F2.
The above-mentioned moment M generates contraction force F3 for contracting a suspension h of the drive wheel c. As a result, in the case of rear-wheel-drive vehicle, squat is apt to occur especially when the vehicle is started, thereby riding comfort, maneuverability and stability of the vehicle are deteriorated.
Moreover, in the conventional anti-squat control, squat which occurs during controlled acceleration slip is not considered. Namely, only the starting squat which occurs when the vehicle is starting can be controlled.
Furthermore, when the vehicle height is adjusted by detecting the inclination of the vehicle by utilizing a vehicle height sensor or the like, responsiveness of the vehicle attitude control is relatively low, because the vehicle height is adjusted after a certain degree of inclination is actually detected.